More by Rima Himelstein, M.D.

Marijuana is the most widely used illegal drug in the world — including by adolescents. New research findings published in the Proceedings of the National Academy of Sciences (PNAS) indicate that teens who become daily marijuana users may be losing IQ points.

Marijuana 101 for Parents

Most parents know the basics about marijuana: it is a mixture of dried and shredded leaves, stems, seeds, and flowers of the cannabis sativa plant. Street names include “pot,” “grass” and “weed.” Most commonly it is smoked in a cigarette-like “joint,” but it is also smoked through a water pipe or “bong”, packed and smoked in a hollowed out cigar (“blunt”), or mixed into baked items. Learn more here. But you may not know that:

The marijuana used today is more potent than it was 30 years ago. Marijuana hasabout 400 chemicals in it, including the mind-altering ingredient, delta-9-tetrahydrocannabinol (THC). Marijuana’s potency depends on the amount of THC it contains. Since 1983, its potency has more than doubled from about 4 percent to 9 percent.

Marijuana use is increasing among teens, and recently, even on school property, according to the CDC Youth Risk Behavior Survey. Almost 40 percent of 8th graders, the youngest teenagers surveyed, reported that marijuana is “easy to get.”

Teens think marijuana is safer than other drugs. Teens are under the misperception that using marijuana is safer than using other drugs and smoking cigarettes. Sometimes when I ask my patients, “Do you use marijuana?” they respond, “Yes,” but when I ask them if they smoke cigarettes they counter, “No, that’s bad for you!” This disconnect is reflected in a national survey, which found that 69 percent of teens think that it’s risky to smoke cigarettes, but only 34 percent think that it’s risky to smoke marijuana.

Long-term effects include cognitive and memory deficits, personality changes (such as amotivational syndrome), anxiety, panic attacks and paranoia; damage to respiratory, reproductive, and immune systems; as well as cancer.

What does the new PNAS study add to what we know? When marijuana use starts in the teenage years, becomes a daily habit, and persists for years, users’ IQ points may be permanently lost. In this study, 1,037 persons were followed from birth to age 38. Marijuana use was assessed in interviews at ages 18, 21, 26, 32, and 38. Neuropsychological testing was done at age 13 (before marijuana use was started) and again at age 38 years.

Here’s the bottom line:

People who began using marijuana during adolescence and were persistent users had a drop in IQ of around 6 points (from 99.68 to 93.93).

People who began using marijuana during adolescence and were persistent users but stopped using marijuana still had a drop in IQ.

People who began using marijuana during adulthood did not have a drop in IQ.

These findings suggest that marijuana may have a lasting neuro-toxic effect on the adolescent’s developing brain.

What can concerned parents do?

Build protective factors: Although risk-taking such as experimenting with drugs may be considered a normal part of adolescence, the consequences may be unacceptable: Addiction, teen pregnancy, and motor vehicle accidents, to name just a few. By building protective factors into a child’s life—such as the consistent presence of a parent during at least one part of the day, commitment to school, religiosity, and involvement in social activities—parents and guardians may be able to reduce the potential for serious risk-taking.

Start talking: Parents and guardians need to bring up the topic and talk with their children about drugs and their risks. If their teen is already using marijuana, pointing out some of the short-term and long-term side-effects of marijuana that they may already be experiencing may help.

Conquer the fable: As part of their development, teens may feel omnipotent and invulnerable to harm—the “personal fable.” This makes it especially important to tell them about the PNAS study and its findings that IQ points may be permanently lost. They may start to realize that the fable is just that and that there’s a reason that marijuana is called “dope.”

Rima Himelstein, M.D., is a Crozer-Keystone Health System pediatrician and adolescent medicine specialist.